Regioselective chemical conversion of a compound with a plurality of different chemical functions requires the protection of all these functions as far as that/those by means of which the chemical reaction is to be initiated. Molecule groups (protective groups) are introduced in order to protect these functions. In conjunction with this, these can be removed in a non-disruptive manner and selectively, with re-formation of the original function. For complex multi-stage syntheses, particularly of natural substances, such as oligopeptides and oligonucleotides, various types of protective groups are necessary. They are characterised by intensely differing conditions of splitting. A system of protective groups in which the individual types are so selectively splittable that all the other respective groups remain unaffected, it termed orthogonal. The principle is the subject of the chemistry of protective groups (see Protective Groups in Organic Synthesis, Greene, T. W. & Wuts, P. G. M. Eds., 2.sup.nd ed., 1991, John Wiley & Sons Inc., New York).
If the type of protective group has a further reactive function, it can be linked covalently and in a stable way with a carrier material for solid-phase synthesis. Then the terms "active group" or "linker group" are used (see e.g. Breitpohl et al. In Tetrahedron Lett. 28 (1987) 5651-5654 and Guibe et al. in Tetrahedron Lett. 30 (1989) 2641-2644). A special type of protective group or also active group is that which must firstly be brought into a labile form by a preceding chemical reaction, and which then in a second step can be split off under very gently conditions (protected protective group--"Safety-Catch" grouping; cf. E.g. Patek in Int. J. Peptide Protein Res. 42 (1993) 97-1176). Although in such a case two reaction steps are required for splitting, such groupings can have great advantages.
(i) it can be very stable against many, even extremely drastic reaction conditions, but can be split by the sequence of two specific extremely mild reaction steps. PA1 (ii) the labile intermediate stage of the protective group can be sufficiently stable to offer good, or better, opportunities for isolation and cleaning the end product. PA1 (i) the protective or active group is to be protected; PA1 (ii) the labile intermediate stage is to be stable under appropriate reaction conditions and permit cleaning of the intermediate products; PA1 (iii) the labile intermediate stage is to be able to decompose in aqueous physiological buffer solution at neutral pH (7) or almost neutral pH (5 to 9), and re-form the original carbamide function, so that the synthesis product can be used directly (without further cleaning) with a free carbamide function in a biocellular or biochemical test experiment. PA1 R.sub.1 --CO means a carbonyl residue which can be provided as a unit for the chain of a peptide, and can have one or a plurality of amino acid residues; PA1 R2 and R3 mean resides of the carbamide which do not participate in their function, whereby R2 and R3 can be identical or different, but are different when one of the two residues means a hydrogen atom; PA1 X means an oxygen atom or a sulphur atom, and PA1 Y means a protective group for X. PA1 a) a compound of the formula C(R.sub.2)(R.sub.3).dbd.X is converted with a compound of the formula R.sub.1 --CO--NH.sub.2 to form a compound with the formula R.sub.1 --CO--NH--C(R.sub.2)(R.sub.3)--XH, and PA1 b) the XH group of the reaction product according to (a) is transferred into an X--Y group, whereby R.sub.1, R.sub.2, R.sub.3, X and Y have the meanings given above.